I know very little about tubes. My question is about tube rolling. In general, are older NOS tubes able to handle higher plate voltage than most modern tubes? In setting the idle bias with only a multimeter and bias pots, assuming that the answer to my first question is yes, is there any general rule of thumb on say 6BQ5/EL84 Telefunkens, Mullards, RCA and the like?
I ask because I recently picked up an old Jolida SJ 101A for cheap and want to fool around with tube rolling. I am aware that running a tube too hot can cherry the plate and that should be pretty obvious visually. What I'm curious about is the wide variation of bias that I have read about people using with the EL84 tubes. Some running 17mV idle bias and others running as much as 40mV with older NOS tubes.
Any thoughts would be appreciated.